The present invention relates, in general, to fiber optic switches which employ cholesteric or chiral nematic liquid crystals and switchable waveplates.
A number of different types of optical switches for switching light between optical fibers are known in the art. Electro-mechanical fiber optic switches have provided the best overall device performance specifications, with insertion losses of 1 dB, crosstalk between unselected fibers of -50 dB, and a 25 ms switching time, howewer, these types of switches require high driving powers and have short life times due to wear, abrasion, and fatigue. Although non-mechanical devices promise longer life, greater reliability, lower power consumption, and shorter switching times, no non-mechanical device has yet fully matched the performance levels of an electro-mechanical switch.
Several liquid crystal materials have been used in non-mechanical optical fiber switches. Nematic liquid crystals have been used in switchable half-wave plates in combination with linear polarization beamsplitters, as well as in switchable total internal reflection structures. Ferroelectric crystals have also been used as switchable half waveplates possessing a fast response speed and bistability. Many of these liquid crystal based optical fiber switches rely on polarization splitting techniques to separate and recombine the two linearly polarized components of an optical beam. To achieve good contrast ratios and low insertion losses, expensive polarization beamsplitters or optical quality calcite crystals are required. The mechanical arrangement of optical components is complicated, and the increased number of optical surfaces requiring anti-reflection coatings further raises device costs.